1. Field of the Invention
The present invention relates to an inspection apparatus for inspecting misalignment of the tips of the external connection terminals of a semiconductor device and a parts mounter using the same.
2. Description of the Related Art
The conventional inspection of misalignment of the external connection terminals of a semiconductor device, particularly inspection of occurrence of bends in easily bendable pin-form external connection terminals forming a pin grid array (PGA), includes irradiating light from a ring-form light source onto an external connection terminal carrying surface of a semiconductor device and picking up a plane image of the external connection terminal carrying surface under the condition that the shadows of the external connection terminals are as weak as possible. The plane image is then processed, based on brightness, so that bright spots are defined as the areas including the tips and then the centers of gravity of the areas are determined as the positions of the tips in a two-dimensional plane. The thus-determined positions of the tips are judged as to whether or not they fall within a reference area, thereby completing the inspection of misalignment of the tips, i.e., of bends in the pin-form external connection terminals.
The conventional inspection can be successfully applied to an external connection terminal in the form of a straight pin standing upright on an electrode pad.
However, the conventional inspection cannot be successfully applied to recent semiconductor devices, such as that shown in FIG. 1, in which cranked external connection terminals 14 normally include a bend because the middle portions extending laterally away from the positions of the electrode pads 10.
Thus, the cranked external connection terminals normally include a displacement of the tips with respect to the positions of the electrode pads 10. Referring to FIGS. 3A and 3B, when a ring-form light source irradiates the cranked external connection terminals (FIG. 3A), the bright Spots B of the electrode pads 10 and the bright spots C of the tips A are very close (FIG. 3B), so that it is difficult to distinguish both spots B and C from each other when determining the positions of the tips A, finally causing a difficulty in providing precise inspection of the misalignment of the tips A.
An object of the present invention is to provide an inspection apparatus for semiconductor devices which enables precise inspection of the misalignment of the tips of external connection terminals formed of cranked metal wires.
Another object of the present invention is to provide a parts mounter including the inspection apparatus.
To achieve the object according to the present invention, there is provided an inspection apparatus for semiconductor devices comprising:
a light irradiation means for irradiating light to a surface of a semiconductor device, the surface carrying external connection terminals formed thereon;
an image pickup means for picking up a plane image of the surface of the semiconductor device by using an optical system to provide image data;
an inspection means for inspecting misalignment of tips of the external connection terminals based on the image data;
the external connection terminals standing on, and being bonded to, electrode pads of the semiconductor device and being bent into crank shapes having respective middle portions extending laterally away from positions of the electrode pads, and
the light irradiation means irradiating light from a side opposite to the laterally extending middle portions of the external connection terminals with respect to the electrode pads.
The external connection terminal is generally formed by ball-bonding a gold or other metal wire to the electrode pad, so that the pad top forms a hemispheric convex surface having one side which reflects the light from the light irradiation means in the direction opposite to the direction in which the middle portion of the cranked external connection terminal extends away from the position of the electrode pad. The other side of the convex hemispheric pad top is not irradiated by the light from the light irradiation unit and is not bright.
Therefore, the bright spot of the electrode pad forms a half-moon shape having a dark side facing the bright spot of the tip of the external connection terminal to provide an increased distance between the bright spot of the electrode pad and the bright spot of the tip of the external connection terminal in comparison with that provided by the conventional lighting by a ring-form light source, so that the bright spots of the tips of the external connection terminals are easily distinguished from the bright spots of the electrode pads to determine the positions of the tips, thereby providing precise inspection of misalignment of the tips.
The optical system is advantageously telecentric on an object side or on both object and image sides. With the telecentric optical system as specified, the light reflected from the tips of the external connection terminals has substantially parallel principal rays, so that any variation in the height of the semiconductor device as an inspection object would cause no inspection errors in the peripheral portion of the object, i.e., parallax errors due to field angle, to provide an improved precision in inspecting misalignment of the tips of the external connection terminals.
According to the present invention, there is also provided a parts mounter comprising:
a holding head for holding and releasing a semiconductor device;
a head transfer unit for three-dimensionally transferring the holding head;
an inspection apparatus for semiconductor devices according to claim 1 or 2 and placed in an inspection position; and
a control unit for controlling the holding head when holding and releasing the semiconductor device, the head transfer unit when transferring the holding head, and the inspection apparatus when inspecting misalignment of tips of external connection terminals so that the semiconductor device is held by the holding head, transferred to the inspection position by the head transfer unit, and inspected for the misalignment by the inspection apparatus.